Welded joints with new properties and provision of such properties by ultrasonic impact treatment

ABSTRACT

Non-detachable welded joints with certain new or improved properties and the provision of such non-detachable welded joints by ultrasonic impact treatment, is described involving conforming to select treatment parameters to control the formation of predetermined properties and thus provide improved qualities and reliability to a joint based on the task to be served by the welded joint. The treatment parameters include repetition rate and length of the ultrasonic impact, pressing force exerted on the ultrasonic impact tool against the surface being treated, and impact amplitude.

RELATED APPLICATIONS

The present application is a continuation-in-part of U.S. Ser. No.10/207,859 filed Jul. 31, 2002, which is a continuation-in-part of bothU.S. Ser. No. 09/273,769 filed Mar. 23, 1999 (now U.S. Pat. No.6,289,736 B1) and U.S. Ser. No. 09/653,987 filed Sep. 1, 2000 (now U.S.Pat. No. 6,458,225 B1), the latter in turn being a continuation-in-partof U.S. Ser. No. 09/288,020 filed Apr. 8, 1999 (now U.S. Pat. No.6,338,765 B1) which is a continuation-in-part of U.S. Ser. No.09/145,992 filed Sep. 3, 1998 (now U.S. Pat. No. 6,171,415 B1). Each ofthe parent applications and patents issued thereon are incorporatedherein by reference.

FIELD OF INVENTION

The invention is directed to welded joints having new strength andprocess induced properties and the process of providing such propertiesto the welded joints by ultrasonic impact treatment (UIT). The weldedjoint of the invention has specific properties providing improvedquality and reliability to the welded joint. In a welded joint, theproperties to be obtained or enhanced are defined based on the task thewelded joint is to serve, such as in the areas of quality, reliabilityand fabricability.

BACKGROUND OF INVENTION

U.S. Pat. Nos. 6,171,415 B1 and 6,338,765 B1 describe ultrasonic impactmethods for treatment of welded structures using pulse impact energy, inparticular ultrasonic impact energy. These patents teach fabrication andrepair treatments for welded structures based on stochastic ultrasonicimpact treatment. The frequency and amplitude of an ultrasonictransducer are basic aspects of the impact. The striction feedbacksignal allows selection of parameters sufficient and necessary to obtaina specified treatment effect.

It has now been found to be desirous to customize properties of a weldedjoint structure. This is in particular beneficial with respect to weldedjoints in view of the particular task and corresponding structure of thejoint to further enhance quality and reliability of the joint.

OBJECTS AND SUMMARY OF THE INVENTION

Accordingly, the present invention is directed to non-detachable weldedjoints with improved properties and the provision of such properties tothe welded joints when subjecting the welded joint to ultrasonic impacttreatment. New structural properties are obtained in the welded joint inview of the particular task to which the welded joint is intended toperform. The description herein is set forth in relation to weldedjoints. However, an equivalent non-detachable welded structure may alsobe treated in accordance with the invention as described herein and theengineering solutions described herein may be applied to any otherequivalent non-detachable welded joints and structures formed thereby.

The invention also involves the selection of parameters for ultrasonicimpact application upon welded joints and structures with new andpredetermined properties.

As with the engineering solutions described in U.S. Pat. Nos. 6,171,415B1 and 6,338,765 B1, the present invention also utilizes stochasticultrasonic impact to treat welded joints. The present invention,however, demonstrates that certain ultrasonic impact treatmentparameters in combination improve technical properties of a weldedstructure, in particular a welded joint. These parameters include (1)the repetition rate and length (or duration) of the ultrasonic impact,(2) the pressure or pressing force exerted on the ultrasonic impact toolagainst the surface being treated and (3) the impact amplitude. The newconditions of ultrasonic impact treatment of the invention also involvean extension of ranges of standard parameters for exciting theultrasonic transducer that generates the carrier ultrasonic oscillatingfrequency in the indenter of the ultrasonic impact tool. A certaincombination of these parameters make it possible to obtain newproperties or modify existing properties in welded joints in view of thetask the joint is to serve. The selected parameters for the ultrasonicimpact treatment control the ultrasonic impact and create the necessaryconditions in order to define new quality and reliability criteria forwelded structures and obtaining welded structural properties suitablefor serving predetermined tasks of the welded structures.

The invention can be utilized for any type of non-detachable weldedstructure, but primarily provides welded joints with properties whichresult in significant performance enhancement. Examples of welded jointstructures of the invention include welded joints in high-strengthsteels; welded joints with stress concentration; welded joints subjectto unbalanced loading, welded joints having defects or damaged areas,such as cracks; welded joints requiring predetermined manufacturingaccuracy; repaired welded joints; welded joints needing repair; lapwelded joints; tack welds for joints; corner welded joints; weldedjoints prone to liquation, coarse grain and pore formation; weldedjoints made with preliminary heating; welded joints having predeterminedstress corrosion resistance; welded joints with holes; welded joints inbrackets or stiffeners; and welded joints prone to martensite formation.

DESCRIPTION OF DRAWINGS

FIG. 1 illustrates, in terms of amplitude and time, vibrations of anultrasonic transducer which cause ultrasonic impact.

FIG. 2 illustrates, in terms of amplitude and time, the force impulserandomly transferred by ultrasonic impact.

FIG. 3 illustrates, in terms of amplitude and time, the lengthenedultrasonic impact obtained using the process of the invention.

FIGS. 4 a and 4 b illustrate fatigue limits of high strength steeluntreated and treated according to the invention, respectively.

FIG. 5 illustrates stress and deformation distribution in a stressconcentration area of material of a welded structure.

FIGS. 6 a and 6 b illustrate, as an example, girders and loadingconditions possible therewith, and the change in the loading conditionsas illustrated through change in the stress concentration area followingultrasonic impact treatment which compensates for dangerous effects ofexternal factors.

FIGS. 7 a, 7 b and 7 c illustrate a socket welded joint before and aftertreatment according to the invention and the effect on stress of thejoint.

FIGS. 8 a, 8 b and 8 c illustrate a defect retardation mechanism forcompressive stresses induced by ultrasonic impact. FIG. 8 a shows thejoint before treatment, FIG. 8 b during treatment and FIG. 8 c aftertreatment.

FIGS. 9 a, 9 b and 9 c illustrate a technique of weld deformationcompensation using, as an example, a symmetric corner welded jointtaking into account directional weld shrinkage. FIG. 9 a illustrates thewelded joint and tolerances thereof before ultrasonic impact treatmentand FIG. 9 b following treatment. FIG. 9 c shows a schematic ofdeformation compensation direction matching.

FIGS. 10 a, 10 b, 10 c and 10 d illustrate a mechanism of action of arepair of a welded joint with crack and stress redistribution due toultrasonic impact treatment.

FIGS. 11 a and 11 b illustrate the formation of a weld joint protectedfrom root crack formation by positive flank angles of the weld metal.

FIGS. 12 a and 12 b illustrate another weld joint formed to be protectedfrom root crack formation.

FIGS. 13 a to 13 e illustrate a spot welded joint before, during andafter ultrasonic impact treatment thereof.

FIG. 14 a illustrates an untreated lap joint; FIG. 14 b illustrates alap joint during treatment; and FIG. 14 c illustrates the lap jointsubsequent to treatment.

FIGS. 15 a and 15 b illustrate a corner welded joint before and aftertreatment in accordance with the invention, respectively.

FIGS. 16 a and 16 b illustrate another corner welded joint before andafter ultrasonic impact treatment.

FIGS. 17 a and 17 b illustrated a weld joint's structural phasehomogeneity (enlarged portion) before and after ultrasonic impacttreatment, respectively.

FIGS. 18 a and 18 b illustrate a weld joint (including an enlargedportion) untreated and after ultrasonic impact treatment to provideactivated crystallization (FIG. 18 b) in the weld joint. FIG. 18 cgraphically represents the treated and untreated weld joints.

FIGS. 19 a and 19 b illustrate a weld joint without and with ultrasonicimpact treatment activated degassing, respectively.

FIGS. 20 a and 20 b illustrate a welded joint with and without hydrogencontent. FIG. 20 c graphically compares a joint with a permissiblehydrogen content and a joint with minimization of residual diffusion ofhydrogen content following ultrasonic impact treatment.

FIG. 21 graphically illustrates the corrosion rate of welded joints ofsteel with high carbon content untreated and treated by ultrasonicimpact in accordance with the invention.

FIGS. 22 a and 22 b illustrate a welded joint with holes at the tips ofa crack before and during ultrasonic impact treatment, respectively.

FIGS. 23 a and 23 b illustrate a welded bracket joint before and afterultrasonic impact treatment, respectively.

FIG. 24 illustrates a diagram of supercooled austenite decomposition insteel.

FIGS. 25 a, 25 b and 25 c illustrate a welded joint before coating andultrasonic impact treatment (UIT), after application of a protectivecoating and before UIT, and after UIT over the coating, respectively.

FIG. 26 illustrates examples of welded joint structures obtainable.

DETAILED DESCRIPTION OF THE INVENTION

Ultrasonic impact treatment utilizes vibrations resulting fromexcitation of an ultrasonic transducer. As shown in FIG. 1, thevibrations occur at a certain amplitude over a defined time. Thevibrations can be forced when the transducer is activated or free duringa pause. The amplitude will lessen during free vibration over time. Asshown in FIG. 2, vibrations as illustrated in FIG. 1 randomly transferthe force impulse to a freely axially moving impacting element orindenter. The forced vibrations of the ultrasonic transducer, as shownin FIG. 1, are interrupted to get information about free vibrations ofthe ultrasonic transducer under load and to correct the oscillatoroperating mode. The source of this information is the feedback signaldelivered from the winding or electrodes of the active element duringpause. It is noted that this principle remains general for all types ofactive materials used in ultrasonic transducers, specificallymagnetostrictive or piezoceramic. To analyze and correct the operationof a generator, and hence a transducer, the striction feedback signal isgenerally used (as described in Russian Patent No. 817931 of Mar. 30,1981). Thus, in order to select ultrasonic impact treatment conditionsin accordance with a task for a particular welded joint, the strictionfeedback signal is used and the technical system tuned for frequency andamplitude of transducer vibrations under off-load and on-loadconditions.

Besides ultrasonic transducer vibrational parameters, being ofimportance in ultrasonic impact treatment, it has now been determinedthat related parameters of the ultrasonic impact are important inobtaining or modifying properties and, thus, characteristics ofnon-detachable welded joints by ultrasonically impacting material of thejoint. Through selection of particular parameters and optimization ofthese parameters, welded joints having predetermined improved propertiescan be obtained. The selection of ultrasonic transducer vibrationalparameters and ultrasonic impact parameters are based on the relatedcharacteristics of the transducer-indenter-treated object oscillatingsystem wherein the characteristics are interdependent with the pressureapplied in treatment against the joint, physical and mechanicalproperties of the joint material, and acoustic properties of the jointitself. FIG. 3 illustrates how the invention results in lengthening ofthe ultrasonic impacts, and thus improving efficiency of the ultrasonicenergy transfer to a treated object in order to obtain new predeterminedproperties in welded joints and structures. Accordingly, the ultrasonicimpact efficiency criteria are direct effects upon the joint materialand the associated length, frequency and amplitude parameters of theultrasonic impact.

Parameters of such an acoustic and mechanical system provide the linkfor obtaining new or modified properties in welded joint structures. Theprocess of determining the correct combination of select parametersinvolves:

-   -   (a) Defining the actual physical properties of the weld and the        material forming a welded joint,    -   (b) Defining conformity of the properties of (a) to properties        desired to meet quality and reliability requirements for a        specific joint,    -   (c) Defining the physical factors resulting from ultrasonic        impact treatment on the welded joint in context of providing the        desired properties to the joint,    -   (d) Defining criteria of the effect of ultrasonic impact        treatment on providing the desired joint properties,    -   (e) Defining conditions of the ultrasonic impact treatment to        provide the desired properties of the joint,    -   (f) Defining the ultrasonic impact treatment conditions in        combination with parameters of the transducer, ultrasonic        impact, indenter, pressure, mechanical properties and acoustic        characteristics of the treated joint material, and    -   (g) Carrying out ultrasonic impact treatment on the joint in        accordance with the definitions established above.

More particularly with respect to the above, to provide non-detachablewelded joints with predetermined new or modified properties byultrasonic impact treatment, the actual physical properties of thewelded joint to be treated are initially determined by conventionaltesting techniques.

The properties desired in a welded joint following treatment must thenbe defined and evaluated as to the difference thereof from theproperties of a welded joint before treatment. This may be achieved bythe present invention referred hereinafter as an algorithm or series ofprocedural steps to achieve the desired end. The algorithm generallyincludes (1) defining conformity of the actual properties of the jointmaterial to specified requirements; (2) defining the physical factorsand the mechanism of ultrasonic impact treatment on a welded joint; (3)defining criteria in determining desired weld joint quality andreliability; (4) defining the basic criteria of the ultrasonic impacttreatment on a welded joint; (5) defining parameters of the ultrasonicimpact treatment for providing non-detachable welded joints with desiredproperties, and (6) determining the results of the ultrasonic impacttreatment on a welded joint to provide predetermined properties. Thealgorithm of the invention is described in further detail hereafter.More particularly, the algorithm involves initially determiningconformity of the actual properties of the non-detachable welded jointto be treated to the properties desired in the joint in view of the taskthe joint is to serve, and conforming to a set of ultrasonic impacttreatment parameters required to obtain the desired properties of thewelded joint.

Physical factors and the mechanism of ultrasonic impact treatment on awelded joint include plastic deformation caused by the low-frequencyimpact; ultrasonic plastic deformation during the impact; amplitude andattenuation (decrement of damping) of the ultrasonic stress wave in thematerial of a given joint, while ultrasonic vibrations of a layersaturated with plastic deformations produced by low-frequency impact andultrasonic plastic deformation occur during the impact; and temperatureand heat rejection rate at the contact point during impacting.

Criteria in determining desired welded joint quality and reliabilityinclude geometry accuracy; residual deformations and their nominaldimension tolerance; residual stresses equilibrated within the volume ofthe joint and structural segments of the joint material; acceptablestress concentration level and configuration of stress raisersresponsible for the load-carrying capacity of the joint; fatigue limitand fatigue resistance under low-cycle and high-cycle reversed andfluctuating loading; and fatigue limit and resistance to corrosion andcorrosion-fatigue failures in aggressive environment under low-cycle andhigh-cycle reversed and fluctuating loading, and properties of thewelded joint material.

Basic criteria of the ultrasonic impact treatment effect on a weldedjoint include the level of induced residual stresses and deformations;relief, roughness and geometry modification of the surface andtransitional areas thereof and modification of material properties inthe treatment area; relaxation and redistribution of residual stressesproduced by the manufacturing technique of a given joint prior toultrasonic impact treatment; and modification of the joint type andconditions of its resistance to service loads.

Parameters of the ultrasonic impact treatment (UIT) for providingnon-detachable welded joints with properties desired include (1)pressure on the ultrasonic impact tool in the range of about 0.1 to 50kg, (2) carrier ultrasonic frequency of the transducer between about 10and 800 kHz, (3) amplitude of ultrasonic vibrations at carrier frequencybetween about 0.5 and 120 μm, (4) ultrasonic impact frequency andself-oscillation frequency of the tool-indenter system between about 5and 2500 Hz with duration of a random ultrasonic impact in the range ofabout 2 to 50 vibration periods at carrier ultrasonic frequency, (5)self-oscillation amplitude of the tool between 0.05 and 5 mm, (6) thelevel of connection between a freely axially moving indenter and atransducer of the tool, which depends on the range of UIT parametersdescribed above, and (7) free ultrasonic impacts with parameters setwithin above-mentioned ranges in accordance with the task, propertiesand sizes of the material and welded joint.

The results of the ultrasonic impact treatment on a welded joint toprovide predetermined properties include at least one of the followingpositive changes: surface roughness and relief of about 0.1 μm andabove; a radius between surfaces of about 0.5 mm and above; the depth ofthe groove along the weld toe line or line between any surfaces in thestress concentration area of up to about 2 mm with the width of thegroove being up to about 10 mm; improvement of material mechanicalproperties in the stress concentration area, as to strength by no lessthan about 1.5 times and impact strength by no less than about 1.2times; plastic deformation, favorable compressive stresses and afavorable relative change in microhardness to a depth of up to about 7mm; distribution of elastic compressive stresses due to plasticdeformation of material in section normal to the surface to the depth ofup to 10 mm; relaxation of process induced residual stresses due toultrasonic fluctuating stress wave with the amplitude of no less thanabout 0.05 of the material yield strength, to a depth of up to about 12mm; favorable residual stresses of the first and second kind on andunder the surface to a specified depth of no less than material yieldstrength and ultimate strength depending on the task definition;compensation for residual process induced deformations by not less thanabout 40% of those which occurred without UIT application withimprovement in stress corrosion resistance by up to about 10 times;improvement in corrosion-fatigue strength by up to about 2.5 times and alife span in a corrosion environment of up to about 20 times undervariable loading; improvement in fatigue limit in air under repeated orfluctuating stress by no less than about 1.5 times and a life span by noless than about 10 times, increasing the strength of a joint by no lessthan 1 category; formation of a white layer and an amorphous structureto a depth of no less than about 50 μm.

The non-detachable welded joints can be made of any joined material withthe use of ultrasonic impact treatment with or without fusion of theinterface of the materials being joined, with or without fillermaterials, and can contain in the aggregate or in any combination theweld material, transition zone of a solid solution of one material inanother and zones altered relative to joined and unjoined materialstructures and modes of deformation. The non-detachable joints may bemade by butt, fillet, lap, narrow-gap or spot welding as well as weldingalong the aperture of structural elements of any given shape with orwithout complete, partial or incomplete penetration, with or withoutedge preparation, and produced by varying means e.g. arc, resistance,laser, electron beam, diffusion, friction, pressure, submerged arc,shielded metal, gas shielded, open and submerged arc welding, weldingusing filler material, open flame of ultrasonic welding, soldering, andthe like.

Particular welded joints of the invention will now be described.

(A) Welded Joints in High-Strength Steels

In practice, the use of high-strength steels in the fabrication ofwelded joints is limited by a low fatigue resistance of the weldedjoints made from such steels as compared to low and average-strengthsteels, namely, low-carbon and low-alloy steels with yield strengths ofa minimum two times as low and fatigue limits up to two times as high asthose of high-strength steels. It is understood in the industry that theconditional boundary between these steels is a yield strength orultimate strength value of up to 500 MPa.

The welded joints of high strength steel of the invention obtained havea fatigue resistance which is at minimum twice as high as that of lowand average-strength steels. This is graphically illustrated in FIGS. 4a and 4 b. FIG. 4 a shows the fatigue limits of a high strength steel 1,a welded joint of low carbon or low alloy steel 2 and a welded joint ofhigh strength steel without ultrasonic impact treatment 3. FIG. 4 bshows the fatigue limits of a welded joint of high strength steel afterultrasonic impact treatment 4 and of a welded joint of low carbon or lowalloy steel after ultrasonic impact treatment 5. As shown, the materialssubjected to ultrasonic impact treatment in accordance with theinvention are significantly improved. The welded joints made of highstrength steels and alloy have a yield strength of σ>500 MPa followingultrasonic impact treatment determined according to the invention andfalling within the parameters as set forth above to provide in thematerial of the welded joint a fatigue limit which is a minimum of 30%greater than that of steels and alloys with σ≦500 MPa.

More specifically, to obtain the above, ultrasonic impact treatment isapplied to an area of hazardous stress concentration at the toe of theweld. Thus, in accordance with the invention, the characteristics of theas-welded joint and the base metal are first determined. Taking intoaccount the need to provide the fatigue limit of the welded jointcomparable to the strength of the base metal of no less than 500 MPa,ultrasonic impact treatment conditions are determined by calculating theimpact energy that suffices to create plastic deformations andcompressive stresses. Ultrasonic impact treatment conditions are thenexperimentally verified and corrected to serve the task. At theoscillating system frequency of about 27 kHz and a tool pressing forceof up to about 10 kg, the ultrasonic impact treatment conditions toprovide a non-detachable welded joint with the desired properties are asfollows: ultrasonic transducer vibrational amplitude during impact ofnot less than about 30 μm, impact frequency in the range of about 80 to250 Hz, tool self-oscillation amplitude of up to about 2 mm, indenterdiameter of about 3 to 6.35 mm, and the average length or duration ofthe indenter being in a range of about 10-35 mm depending on the weldedjoint type. The above ultrasonic impact treatment conditions areresponsible for strengthening hazardous tensile stress concentrationarea and creation therein of favorable compressive stresses to a depthof no less than about 2 mm, whose magnitude at the surface is greaterthan the yield strength and fatigue limit of the base material by afactor of up to about 1.5. In such a case, the stress concentration areaafter ultrasonic impact treatment attains the configuration of a regulargroove with a depth up to about 1 mm, which is formed due to plasticdeformation caused by the ultrasonic impact and provides a smoothtransition between the weld and the base metal.

Thus, the inclusion of high-strength steels in the fabrication of weldedstructures and in the resulting welded joint is available.

(B) Welded Joints with Stress Concentration

Physical and mechanical properties of the material at a weld toe of ajoint, the nature of operating stresses and their distribution at astress concentration area are the basic strength and fatigue resistancecriteria for welded joints with stress concentration together with theconcentration factor that depends on the geometry of the transitionbetween the weld and base metal at the weld toe.

Weld joints are obtained according to the invention by ultrasonic impacttreatment of the stress concentration area to improve the strength,ductility and impact strength of the treated welded joint material abovenominal values relative to untreated material forming the welded joint.In addition, the welded joint is modified and adapted to external loads,since the ultrasonic impact treatment of the stress concentration areaperformed induces favorable residual compressive stresses in the treatedarea.

The condition, characteristics and properties of the treated area aredetermined by the features of ultrasonic and impulse plasticdeformations, which are dependent on the amplitude and length ofultrasonic impacts and their repetition rate during ultrasonic impacttreatment. As a result, the ultimate strength and fatigue limit of theweld joint material in the stress concentration area are greater thanthose of materials forming the weld joint.

The mode of deformation of the weld joint under such conditions isdefined by the residual stresses and equivalent plastic and elasticdeformations. The favorable residual compressive stresses in the area ofultrasonic plastic deformations due to ultrasonic impact treatment arenot less than the greater nominal yield point of the materials. Elasticdeformations and respective elastic stresses decrease exponentially inthe depth of the treated material from the maximum of the residualcompressive stresses equilibrating the elastic stresses while the leveland distribution of the residual and elastic stresses on and under thesurface are established to compensate for environmental effect andoperational stresses.

Stress and deformation distribution in the stress concentration area areshown in FIG. 5 together with the change in material properties in thisarea as a result of ultrasonic impact treatment performed in accordancewith the algorithm described herein.

It is well-known that hazardous stress concentration is generallylocalized at a weld toe. This is due to the unfavorable sharp transitionbetween the weld and the base metal, the presence in this zone ofpronounced welding defects (such as overlaps, irregularities, undercuts)as well as due to tensile residual stresses caused by weld shrinkage oncooling.

In accordance with the invention, ultrasonic impact treatment produces asmooth transition between a weld and a base metal by forming a groovewith radiuses at its boundaries of about 0.5 mm and greater, with widthsof greater than zero and up to about 10 mm and depths of greater thanzero up to about 2 mm depending on the metal thickness and the weld toeangle. Ultrasonic impact treatment conditions define the relief, grooveroughness (not less than Ra=75 μin), the magnitude and the nature ofinduced compressive stresses (not less than the material's ultimatestrength), the effect thereof to a depth of not less than about 2 mm inthe plastic deformation area and not less than about 5 mm in the elasticdeformation area, and residual welding stress relaxation to a point notgreater than about 20% of the original state.

The parameters to provide the welded joint include an ultrasonicvibration amplitude during impact of greater than zero and up to about50 μm at a frequency of greater than zero and up to about 80 kHz, impactfrequency of greater than zero and up to about 500 Hz, toolself-oscillation amplitude of about 0.2 mm and greater, the off-dutyfactor of impact impulses of greater than zero and up to about 0.5, apressing force of at least about 3 kg and as a consequence of the above,impact energy which is equivalent and sufficient to create compressivestresses and modify material ultimate strength properties in the stressconcentration area to be greater than the original stress and strengthproperties and sufficient to compensate for external operational forces.

Ultrasonic impact treatment of carbon steels performed in accordancewith the method under the above-mentioned conditions increases thefatigue limit of a welded joint as a result of a combined action of thephysical factors set forth above, as well as the removal of weldingdefects by plastically deforming the welded joint material.

(C) Welded Joints Subjected to Balanced and Unbalanced Loading

A primary requirement that defines the ability of welded joints toresist failure under balanced and unbalanced loading in the originalcondition is the unbalanced nature of the load on these joints afterultrasonic impact treatment to obtain properties in accordance with theinvention. However, the final stressed state of the welded joint willalways depend on the condition of external loading on the weld joint. Onthis basis, ultrasonic impact treatment of the weld joint is performedin accordance with the algorithm of the invention concurrently withbalanced or unbalanced loading on the joint, which is close to actualloading.

The level and nature of external loading on a given weld joint andrelated parameters of ultrasonic impact treatment performed aredetermined and matched by the condition of adequacy to compensate forthe effect of factors causing crack formation during operation of agiven weld joint.

The procedure of rating the ultrasonic impact treatment adequacy as apart of the invention can be as set forth below.

Initially, the varying loading, which is adequate to the actual loading,is applied to a sample or the actual welded joint in the as-weldedcondition and stresses or equivalent deformations due to the loading aremeasured by any conventional means. By calculating the required impactenergy, the parameters of ultrasonic impact treatment are thendetermined to compensate for the stresses or deformations. Thereafter,ultrasonic impact treatment is applied together with the varying loadingand the level of compensation for hazardous operational stresses ordeformations is established by the measuring procedure used before. Ifrequired, design parameters of ultrasonic impact treatment are correctedto compensate for stresses or deformations as defined by the task theweld joint is to perform.

The ultrasonic impact treatment of a welded joint applied in parallelwith the load can be performed in the free state on an unfixedstructure, in a rigid contour on a fixed structure, or under constant,variable and balanced loading.

To solve problems as above described, the parameters of ultrasonicimpact treatment to provide welded joints made from carbon structuraland stainless steels, and aluminum and titanium alloys with the desiredproperties includes ultrasonic vibration amplitude during impact ofgreater than zero and up to about 50 μm at a frequency of greater thanzero and up to 80 kHz, the impact frequency of greater than zero and upto 500 Hz with the prevailing impact duration on average of no less thanabout 1 ms, the tool self-oscillation amplitude of about 0.2 mm andgreater, the pressing force of no less than about 3 kg and as aconsequence of the above, the impact energy equivalent and sufficient tocreate compressive stresses and modify material ultimate strengthproperties in the stress concentration area to be greater than theoriginal compressive stresses and strength properties and are sufficientto compensate for external operational forces.

The change in the loading condition as a result of concurrent ultrasonicimpact treatment which results in compensation for the dangerous effectsof external factors is shown in FIGS. 6 a and 6 b through exemplarygirder structures. FIG. 6 a shows girders under different stressloadings. Girder 10 illustrates a girder under static loading Fc. Girder11 is under cyclic, fluctuating or dynamic loading Fv. Girder 12 isunder complex loading, i.e., Fc+Fv. FIG. 6 b shows the initial stressedstate in the stress concentration area for each of girders 10, 11 and 12as compared to the stressed state in the same girder after ultrasonicimpact treatment.

Another exemplary structure is a so-called “socket weld joint” as shownin FIG. 7 a. In FIG. 7 a, 20 indicates a socket welded joint and 21denotes the ultrasonic impact tool in treatment of the weld for thejoint. The feature of this “socket weld joint” which is unique is thatthe joint is generally used in structures having both fluctuating andalternating loading with a relatively small thickness in the materialforming the welded joint. In this case, ultrasonic impact treatment ofthe stress concentration area in accordance with the invention forms agroove of dimensions and depth not greater than about 0.15 mm ofthickness of the treated material. FIG. 7 b illustrates the joint beforeand after ultrasonic impact treatment. Following treatment, the weldedjoint has a radius 22 of a minimum of about 0.5 mm, width of greaterthan zero and up to about 10 mm, depth of greater than zero and up toabout 2 mm and about 0.15 mm of web thickness when the overall thicknessis about 4 mm.

Thus, the modification of the material properties in the stressconcentration area results in a specific level of compressive stressesinduced in the stress concentration area of the joint. Conditions forcreating such stresses and groove dimensions related with weld jointdimensions and the thickness of materials forming the socket weld jointgive the socket weld joint in the aggregate an excellent breakingstrength under fluctuating and cyclic loads that induce stresses abovethe yield strength of the joint material in the stress concentrationarea. FIG. 7 c comparatively shows the cycle stress of the joint beforeand after ultrasonic impact treatment. Accordingly, the loadingcondition and ultrasonic impact treatment of the weld toe and theload-carrying component on the side of constant loading and/orlocalization of varying loading, initiate the ultrasonic plasticdeformation, creation and distribution of compressive stresses andformation of a transition between the weld and the base metal so as tocompensate for the influence of static or cyclic or varying stressesthat cause the formation of in-service cracks due to the stressconcentration above the yield point of the base metal along the weld toeand/or in the root.

(D) Welded Joints with Defects and Damaged Areas (Including Cracks)

The practice of fabrication and operation of welded structures presentsan independent group of problems associated with the improvement of thelife and reliability of welded joints which have welding defects,material structural defects, meso-structure damages and cracks.

The benefits of ultrasonic impact treatment performed in accordance withthe invention makes it possible to provide properties in welded jointsin which the above defects are detected so as to result in a reliablejoint. Of importance for weld joint modification in such instance arethe ultrasonic plastic deformation, deformations due to external forceimpulse (impact) and residual compressive stresses that are introducedinto the material of the welded joint wherein such are within theabove-described parameters for these factors of ultrasonic impact effecton the material condition.

Of critical importance in modifying defective welded joints isultrasonic plastic deformation, i.e., deformations caused by the impactand residual compressive stresses introduced into the material of thewelded joint that cover the above-described defects and retard theirdevelopment under external forces due to operational loads.

The crack is the most common example of a hazardous defect in a weldedjoint material. Using differing crack sizes, in fact, allows fordefining the internal condition and simulating the initial conditions orstages of failure produced by other types of defects under externalforces.

The hazardous area of all types of welding defects, including cracks, isthe stress concentration area, as shown in FIGS. 8 a-8 c. Also shown inFIGS. 8 a-8 c is the defect retardation mechanism in the field ofcompressive stresses caused by the ultrasonic impact treatment. In FIG.8 a, 30 denotes a defective welded joint containing a crack beforeultrasonic impact treatment and the stresses present in relationthereto. FIG. 8 b illustrates treatment of the defective area with anultrasonic impact tool 31 to create a compressive field. FIG. 8 cillustrates the welded joint 32 following ultrasonic impact treatmentand the change in the stresses present therein (compare FIGS. 8 a and 8c).

A defect presents the severest hazard when the tension vector isperpendicular to the plane on which the greatest defect area isprojected. In the case illustrated in FIGS. 8 a-8 c, the crack peripheryoutlines the stress concentration area. When the defect is subjected tothe compressive stress field by means of ultrasonic impact treatment inaccordance with the invention, this makes it possible to compensate forunfavorable tensile stresses in the stress concentration area anddisplace them to a region of the material where the stress concentrationhazard is unlikely.

In this instance, ultrasonic impact treatment is localized on thesurface, whose dimensions suffice to displace possible tensile stressesaway from the possible stress concentration at a distance sufficient tomaintain resulting compressive stresses under unfavorable conditions ofexternal force action. The dimensions of this surface are determinedduring simulating defect development and retardation conditions asdescribed herein. Ultrasonic impact treatment parameters in this case toprovide the desired welded joint include the following: tool pressingforce of greater than zero and no greater than about 10 kg; ultrasonicimpact frequency of greater than zero and no greater than about 500 Hz;prevailing duration of ultrasonic impact of no less than an averageabout 1 ms; ultrasonic carrier frequency of greater than zero and up toabout 100 kHz depending on the properties of the material being treatedand the surface condition requirements; ultrasonic oscillation amplitudeof the indenter during impact of no less than about 30 μm; and impactamplitude of no less than about 0.2 mm. The impact energy defined inaccordance with the process and expressed by the above parameters andcorresponding indenter mass is set so as to produce compressive stressesin the plastic deformation area to a depth of no less than about 2 mmand in the elastic deformation area, to a depth that suffices tocompensate for the residual effect of tensile stresses.

New properties and welded joint material conditions so obtained allowcompensation for the effect of the dangerous stresses resulting fromoperational loading on a given welded joint and thus also theretardation of the defect development when the joint is in service.

(E) Welded Joints with Specified Requirements to Manufacturing Accuracy

Geometric accuracy of welded joints is a primary quality and reliabilitycharacteristic. Ultrasonic impact treatment in accordance with theinvention is characterized by a system of features that guaranteesmeeting this fundamental technical requirement. These featuresessentially include ultrasonic relaxation (of stresses anddeformations), ultrasonic and impulse plastic deformation (materialredistribution), and creation of compressive stresses (redistribution oftensile and compressive stresses and deformations).

Thus, four ways to obtain a specified accuracy in a welded joint are asfollows: (1) ultrasonic impact treatment performed in accordance withthe invention using a rigid attachment (fixed position) and ultrasonicrelaxation of residual welding stresses caused by fixation, (2) weldingwithout fixation, ultrasonic and impulse plastic deformation of the weldand base metal in the joint area in accordance with the invention,material redistribution in the joint, compensation for shrinkage andthus welding deformations, (3) combining (1) and (2) above in theultrasonic impact treatment, and (4) dividing (differentiation of) weldshrinkage by directions and ultrasonic impact treatment taking intoaccount compensation for joint deformations in these directions.

The above examples of obtaining welded joints with specifiedconfiguration accuracy requirements are applied over hot (above ambienttemperature) metal during welding or when the weld is cooled down orover cold (at about ambient temperature) metal after welding dependingon the task and specific conditions of its solution.

The technique of weld deformation compensation is shown in FIGS. 9 a, 9b and 9 c using, as an example, a symmetric corner welded joint takinginto account a directional weld shrinkage. FIG. 9 a illustrates thewelded joint 40 and the tolerances therein. FIG. 9 b illustrates thewelded joint after ultrasonic impact treatment with ultrasonic impacttool 41. Deformations and tolerances are denoted in FIG. 9 b as follows:a and f each indicate residual deformation after ultrasonic impacttreatment, b and e each indicate tolerance, and c and d each indicateresidual welding deformation. FIG. 9 c illustrates schematicallydeformation compensation direction matching. While residual weldingdeformations in the joints are compensated for by either creating arigid attachment with subsequent ultrasonic relaxation of residualwelding stresses or ultrasonic and impulse plastic deformation andredistribution of the weld metal or by a combination of these effects,and, thus, in so doing match the direction and magnitude of plasticdeformation of the weld metal with the ratio between its longitudinaland transverse shrinkage depending on the welded joint type and weldingprocess.

During compensation for deformations in directions specified by thetask, the principle is used of selecting the ultrasonic impact treatmenttool marks overlap coefficient (K_(o)). The greatest value of K_(o)corresponds to the direction of greater residual deformations thatshould be compensated so as to provide the specified accuracy, while thesmallest value of K_(o) corresponds to the direction of smaller residualdeformations. The residual deformations in various directions correspondto the shrinkage of weld metal and near-weld zone in these directions,and deformation compensation corresponds to the sum of cumulativedisplacements of local volumes of weld metal and near-weld zone causedby plastic deformation due to ultrasonic impact treatment. Taking K_(o)to be positive and equal to the relationship between the indentationdiameter difference and the indentation center-to-center distance whenthe surface is fully covered with tool marks, and the ratio ofinterindentation distance to indentation center-to-center distancecorresponds to negative overlap coefficients during intermittenttreatment, then ultrasonic impact treatment provides control ofdeformation compensation in specified directions within the range ofvalues, for which the following is true: 1>K_(o)>−1.

Thus, at a tool or workpiece travel speed of about 90 m/min, K_(o)becomes positive even at an ultrasonic impact frequency of 500 Hz andthe indentation diameter of 3 mm. The actual ultrasonic impact treatmentspeed, however, is within the range of greater than zero and up to about5 m/min. This emphasizes the reliability of ultrasonic impact treatmentin accordance with the method of the invention and possible control ofK_(o) within the wide range of treatment conditions, i.e., pressingforce on the tool of about 4 kg and above, impact frequency of about 100Hz and above, impact amplitude of about 0.2 mm and above, impactduration of about 1 ms and above, carrier ultrasonic frequency of noless than about 15 kHz, ultrasonic vibration amplitude during impact ofno less than about 30 μm when steels and high-strength alloys aretreated and greater than zero and no greater than about 30 μm whenaluminum alloys and metals with a yield strength of up to 350 MPa aretreated.

(F) Repaired Welded Joints

Repaired welded joints covers a wide area of fabrication and operationof welded structures, e.g., repair of weld defects, failures and cracks,strengthening structures and elements thereof, as well as providingadditional improvement in structural stability and load-carryingcapacity and correcting structural configuration in the process offabrication and operation. At the same time, repairs of welded jointsare a source of residual welding stress, deformation, and stressconcentration area and, thus, unregulated metal fatigue.

Ultrasonic impact treatment conducted in accordance with the inventionsolves these problems and results in welded joints repaired to haveimproved properties, i.e., a level of residual stresses not greater thanabout 0.5 of the yield strength of the welded joint material, residualwelding deformations not greater than 100% of the dimensional tolerancespecified for a given joint, and fatigue resistance of not less thanthat of the base metal of the given welded joint.

The mechanism of action on a repaired welded joint, and cracks andstress redistribution due to ultrasonic impact treatment are illustratedin FIGS. 10 a to 10 d.

As shown in FIG. 10 a, the crack in a plane perpendicular to tensileforces or in a spatial surface close to the plane creates aconcentration of stresses that is many times greater than normal designstresses due to such forces.

A repaired welded joint somewhat improves the situation. However, itproduces a new residual tensile stress concentration at the ends of therepair welding caused by the longitudinal shrinkage of the welddeposition (FIG. 10 b).

Ultrasonic impact treatment in accordance with the invention (FIG. 10 c)redistributes unfavorable residual tensile stresses that are replaced bycompressive stresses in the hazardous weld deposition area (FIG. 10 d).As this takes place, tensile stresses move into the region of normalstresses that is safe for the welded joint load-carrying capacity andcan be calculated using standard procedures.

Ultrasonic impact treatment of a repaired welded joint, as defined bythe task served by the joint, is applied in the course of welding to themetal being cooled and to the cold metal.

Thus, to improve the quality of the weld metal and its resistance tostructural defect formation, ultrasonic impact treatment in accordancewith the invention is done during welding. In order to compensate forresidual welding deformations and stresses localized in the repairwelded area, ultrasonic impact treatment in accordance with theinvention is done upon the metal being cooled. Ultrasonic impacttreatment is done on the cold (ambient temperature) metal to hardenwelded joint metal, create favorable compressive stresses in hazardousareas, and replace and relax hazardous tensile stresses.

In doing so to provide the welded joint, the pressure upon theultrasonic tool during manual treatment of steels is about 3 kg andabove, which may increase up to 20 kg in the case of mechanizedtreatment, the impact frequency is not less than about 80 Hz, the impactfrequency is not less than about 0.2 mm, the impact length is not lessthan on average about 1 ms, the carrier frequency of indenter ultrasonicvibrations is about 15 kHz and above, the ultrasonic vibration amplitudeduring impact is not less than about 20 μm when hot (above ambienttemperature) metal is treated and not less than about 30 μm whentreating metal being cooled and cold metal. When weld deposits ofaluminum alloys are treated, the ultrasonic vibration frequency isreduced by up to 40% subject to the strength of material.

(G) Corner Joints with Incomplete Penetration Protected from RootCracking

A welded joint protected against root cracking and having aload-carrying capacity is obtained by selecting type and dimensions of aweld joint with complete, partial or incomplete penetration. Achievingsuch is particularly difficult when the joint has partial or incompletepenetration.

The cause of root crack formation is primarily associated with the flankangle of the weld metal with the web end and flange plane in a gapbetween them, as may be exemplified by a corner joint. In the case of anegative (acute) flank angle, the crack formation directly results fromthe stress concentration in this area of the welded joint.

Ultrasonic treatment of a weld joint, performed during welding, solvesthis problem by changing heat exchange conditions at the boundarybetween the molten metal and the solid metal in the root of the weld.This phenomenon may be explained as follows. Ultrasonic impact duringwelding causes an impulse and ultrasonic stress wave to propagate in theweld metal and thus the molten metal. As a result, strong acoustic flowsare formed at the molten-solid metal boundary in the weld root thatcontribute to heat exchange activation and hence greater penetration ofthe surface of metal forming the gap between web and flange in thisarea. Thus, based on the procedure invention, an instrument to controlthe penetration configuration of the web and flange metal in the weldroot may be provided, thereby resulting in a substantially newappearance of a welded joint having positive (obtuse) flank angles ofthe weld metal with the flange surface and web end, which, in turn,insure that a given welded joint is resistant to stress concentrationand fatigue crack formation in the weld root.

The formation of a weld joint protected from root crack formation bypositive (obtuse) flank angles of the weld metal with the web and flangemetal in the gap between them is shown in FIGS. 11 a and 11 b. FIG. 11 aillustrates a weld 50 made without ultrasonic impact treatment. FIG. 11b illustrates a weld 51 subjected to ultrasonic impact treatment usingan ultrasonic impact tool in an initial operating position 52 duringwelding and a continuing operating position 53.

The selection of the tool angle and ultrasonic impact treatment areas,as shown in FIGS. 11 a and 11 b, allow formation in the molten pool ofacoustic flows specifically directed relative to the pool boundaries.This, in turn, offers possibilities for control of the flange and webmetal fusion penetration intensity in directions where the weld metalfavorably meets the base metal.

Thus, when the flange side face is subjected to ultrasonic impacttreatment (operating position 53 FIG. 11 b), the prerequisites arecreated for better fusion of the flange metal as compared to the web. Aclose effect can be obtained by increasing the tool angle relative tothe flange plane by more than 450 (the position 52 in FIG. 11 b). Achoice of treatment conditions, tool angles and positions duringtreatment depends on the welding process, material and dimensions of awelded joint. The above-mentioned preferred ultrasonic impact treatmentconditions to provide welded joints of this type made of carbon steelsinclude: tool pressing force of about 3 kg and above during manualtreatment, greater than zero and up to about 25 kg during mechanizedtreatment; impact frequency of greater than zero and up to about 800 Hz;impact amplitude of about 0.2 mm and above; ultrasonic vibration carrierfrequency of about 18 kHz and above; ultrasonic vibration amplitudeduring impact of greater than zero and up to 20 μm in a temperaturerange of above about 400° C. and not less than about 30 μm in atemperature range below about 400° C.; and ultrasonic impact duration ofon average of not less than about 1 ms.

With favorable redistribution of the weld metal between the flange andthe web, ultrasonic impact treatment in accordance with the inventionreduces residual welding stresses by a minimum of 40% of standard modeof deformation of the as-welded joint.

Concurrent with the heat exchange activation effect described above, theultrasonic impact in accordance with the invention initiates a surfacetension reduction effect for the molten metal and, as a consequence ofthis phenomenon, increases the fluidity of the molten metal. That is,ultrasonic and impulse stress waves are transferred to materials beingwelded through the weld metal as a result of the ultrasonic impacttreatment and increase the yielding and hence the flowability of themolten metal on the web and flange ends in the gap between them. Thetemperature of the molten pool, activated by the acoustic flow,additionally fuses the edges, forming a concave meniscus similar to thatin capillary as shown in FIGS. 12 a and 12 b. It was established thatthe molten metal fluidity increases within a wide range of ultrasonicvibration carrier frequencies of up to 300 kHz and ultrasonic impactrepetition rates of up to 2500 Hz. Ultrasonic impact treatmentparameters are defined in accordance with the process of the inventiondepending on the properties of welded materials and consumables, thetype and sizes of welded joints, the welding process and conditions. Inthe schematic representation of a welded joint as shown in FIGS. 12 aand 12 b, FIG. 12 a shows a weld 60 not subjected to ultrasonic impacttreatment and the crack formed therein. FIG. 12 b shows a weld 61subjected to ultrasonic impact treatment. The meniscus in the weld rootis denoted by 62. The ultrasonic impact tool is shown in an initialoperating position 63 on the weld and in a continuing operating position64 during treatment of the weld. The corner welded joint, withincomplete and/or partial penetration, made with ultrasonic impacttreatment conducted within the parameters of the invention during makinga root run over the weld metal, flange or web, results in the moltenmetal filling the gap (under ultrasonic impacting) between the stiffeneror web end and the flange or web plant with or without diffusion oradhesion bonds between the weld and the base metal in the gap producinga meniscus 62 and fusing of the sharp edges upon solidification fromsmooth transitions between base and weld metals, thereby increasing theresistance of a given welded joint to stress concentration effect andfatigue crack formation in the root of the weld.

Thus, one further mechanism makes possible positive (obtuse) flankangles of the weld metal with the web end and flange surface as a resultof ultrasonic impact treatment in accordance with the invention. Thisexplains how a new welded joint is formed that is protected from rootcrack formation due to stress concentration and fatigue.

(H) Spot Welded Joints

A specific task associated with the need to increase quality andreliability of a welded joint based on fatigue resistance criterionrelates to spot welding. A primary problem is that the danger zone inthe weld joint area is inaccessible for conventional stressconcentration treatment techniques. This necessitates modifying a modeof deformation of a welded joint across the whole thickness of thematerials being welded. Thus, the dangerous heat affected zone must beconsidered to include stress raisers and represent a circle or ring withan average diameter that is equal to the diameter of a circle along theboundary of a welded joint.

A spot welded joint made using ultrasonic impact treatment in accordancewith the invention features a high level of ultrasonic plastic andimpulse deformation across the whole metal thickness in the weld area,the fatigue limit being a minimum of about 1.3 times greater than thatof an untreated joint and having an ultimate strength of not less thanthat of the base metal.

A schematic representation of a spot welded joint is shown in FIGS. 13a-13 e. FIG. 13 a illustrates at 70 an untreated spot welded joint andstresses in relation thereto. FIG. 13 b shows an ultrasonic impact tool71 in treatment of a spot weld in conjunction with a stop plate 73. InFIG. 13 c, two ultrasonic impact tools 71 and 72 are utilized inrelation to a spot weld. FIG. 13 d is a close-up of the point of contactof impact from a stop plate or tool 74 and tool 75 as to the spot weld.FIG. 13 e shows at 76 a treated joint and stresses in relation thereto.

Ultrasonic impact treatment of a spot welded joint can be done duringwelding (when the welding electrode at the same time presents thevibration velocity concentrator or indenter) and after welding. Theindenter can have a round, flat and circumferential working surfacedepending on the welded joint size and its post-welding condition.

In fact, ultrasonic impact treatment can be applied using passive oractive resonance acoustic decoupling, passive non-resonance acousticdecoupling and a rigid stop block serving as an “anvil”. It means thatplastic deformations in the welded joint area may be formed sequentiallyfrom each side and simultaneously from both sides.

As shown in FIG. 13 a, the risk area of the spot welded joint, where themaximum tensile stresses operate, is localized at the “spot weld”boundary and is positioned in the operational stress criticalconcentration zone.

Ultrasonic impact treatment in accordance with the invention completelysubjects the welded joint to the favorable compressive stress area anddisplaces the tensile stress area to the zone without any structuralprerequisites for stress concentration.

Thus, based on the experimental data, ultrasonic impact treatment inaccordance with the invention, increases the fatigue limit of a spotweld by at least about 1.3 times and improves the fatigue resistance,yield points, ultimate strengths and impact strength to the level notbelow that of the base material.

To obtain spot welded joints made of carbon steels and aluminum alloys,ultrasonic impact treatment conditions include the following and varywithin the described amounts based on the joint type and material:ultrasonic impact frequency of not less than about 80 Hz, impactduration of not less than on average about 1 ms at an amplitude of notless than about 0.2 mm, indenter ultrasonic vibration carrier frequencyduring impact of greater than zero and up to about 100 kHz, ultrasonicvibration amplitude during impact in a range of from about 5 to 40 μm,and tool pressure from about 3 to 30 kg. The stabilization of theresonance frequency of the system “tool-welded joint within a structure”during welding with ultrasonic impact treatment or during ultrasonicimpact treatment is the method treatment termination criterion for suchtypes of welded joints.

(I) Lap Welded Joints and Tack Welds

Lap or tack welded joints are extremely prone to cracking at weld endswith cracks quickly propagating on short weld portions. Crack formationin these joints is mainly due to welding defects, unfavorable weld toeangles, stress concentration, the loss of the local stability andstrength of a joint, and fatigue. These problems can be solved bycreating a welded joint, which is subjected to ultrasonic impacttreatment in accordance with the invention to result in the formation ofa smooth transition between the weld and base metal. At the same time,such transitions at the tack weld end and along the weld toe line aresubjected to ultrasonic plastic deformation, while the fatigue limit ofthe tack weld is a minimum about 1.3 times greater as compared to theuntreated condition, and the fatigue resistance, ultimate strength andimpact strength are not less than that of the base metal. A schematicrepresentation of a welded joint and the mode of deformation thereof dueto ultrasonic impact treatment is shown in FIGS. 14 a to 14 c. FIG. 14 ashows an untreated lap joint and stresses 80 in relation thereto. FIG.14 b illustrates a lap joint during treatment with an ultrasonic impacttool 82 to create compressive stress areas as denoted thereon. FIG. 14 cillustrates the treated lap joint 84 and the stresses associatedtherewith.

More specifically, FIG. 14 a shows that maximum tensile stresses arelocalized at tack weld ends due to longitudinal and, to a lesser extent,transverse weld shrinkage. This situation is aggravated by the fact thatthe tack weld end area coincides with the operational stressconcentration area.

Ultrasonic impact treatment in accordance with the invention changes thenature of the welded joint mode of deformation, redistributes tensilestresses, replaces these by compressive stresses and displaces tensilestresses due to operational loads to the welded joint region wherestress concentration is unlikely to occur. Ultrasonic impact treatmentin accordance with the invention improves the resistance of a givenwelded joint to formation of cracks caused by the stress concentrationdue to design features of a given joint and metal fatigue under theunfavorable nature of variable and reversed loading cycles.

Thus, in parallel with residual stress redistribution, the improvementof a given welded joint resistance to crack formation is also achievedby modifying material properties of the welded joint during ultrasonicplastic deformation thereof, as shown in FIGS. 14 a-14 c.

Parameters of ultrasonic impact treatment in accordance with theinvention which provide the desired welded joint include the following:ultrasonic impact frequency of greater than zero and up to about 2000Hz, ultrasonic impact length of not less than on average about 1 ms,impact amplitude of not less than about 0.2 mm, indenter ultrasonicvibration carrier frequency of about 18 kHz and above, indenterultrasonic vibration amplitude during impact of not less than about 25μm for carbon steels and not greater than about 30 μm for aluminumalloys, tool pressure against a treated surface of about 3 kg and above.

(J) Corner Welded Joints

It is a difficult technical problem to obtain manufacturing accuracy andhigh fatigue resistance of corner welded joints with a groove varyingalong the joint perimeter, as well as with a varying flank angle of lessthan 90° and complete weld penetration. This problem is aggravated byspecific welding stress and deformation distribution present, as well asthe joint fatigue limit dependence on the geometric conditions of theformation of a complex oriented in the space joint along the weldperimeter.

Ultrasonic impact treatment performed in accordance with the inventionduring welding and over cold metal makes possible a specifieddimensional accuracy along the perimeter of such a complex joint andincreases fatigue limit at a minimum by a factor of 1.3. A schematicrepresentation of a corner welded joint with a groove varying along theperimeter and an angle of less than 90° treated by ultrasonic impacttreatment is shown in FIGS. 15 a and 15 b. The welded joint is denotedas 90 and the weld as 91. The ultrasonic impact tool 93 is shown indifferent weld treatment positions.

Corner welded joints with an angle between the web and flange of <90°and with a through or incomplete penetration are widely used, whichbrings to the forefront the problem of technical cost minimization,providing therewith a dimensional accuracy and appropriate fatigue limitand life span. Ultrasonic impact treatment in accordance with theinvention solves this problem by ultrasonic and impulse compensation forlongitudinal and transverse weld shrinkage, symmetric angle deformationof the flange relative to the web, material properties and conditionmodification in the stress concentration area. This provides for a weldjoint wherein the angles between the web and flange are <90°, andobtaining a specified joint dimensional accuracy as well as increasedfatigue limit and life span not less than a factor of 1.3 and 10respectively.

A schematic representation of a welded corner joint in accordance withthe invention is shown in FIGS. 16 a and 16 b. FIG. 16 a shows the workpieces 100 for forming a corner prior to welding. FIG. 16 b illustratesthe work pieces including corner welds 101 being treated by ultrasonicimpact tools 102. Following ultrasonic impact treatment, modificationsare present in the properties of the treated material. Deviation fromspecified dimensions after ultrasonic impact treatment is within thetolerances for longitudinal and cross deformations. The fatigue limit ofthe welded corner joint after treatment is a minimum of 1.3 timesgreater over that of a welded corner joint in an untreated condition.The life span of the welded corner joint after treatment is a minimum of10 times greater than that of the welded corner joint in an untreatedcondition.

Thus, the fabrication and maintenance of corner welded joints withvarying and “constant” groove beveling angles, as shown in FIGS. 15 a-15b and 16 a-16 b, is associated with the need to search for engineeringsolutions that through minimum production costs provide, on one hand,the requisite accuracy of such joints and on the other hand, a specifiedlife thereof.

The accuracy of corner welded joints should ensure their servicereliability, design load-carrying capacity and external loadingresistance. The endurance of the welded joints should ensure a life timeexpressed through the resistance of the welded joints to varying andreversed loads.

The welded joint accuracy is generally achieved by heat treatment andusing a costly conductor tool set. The endurance of the welded joint isachieved through special approaches to selection of the base metal andwelding consumables, greater weld dimensions and the heat treatment forresidual stress reduction.

Ultrasonic impact treatment in accordance with the invention minimizesproduction costs, eliminates the need for heat treatment and the use oflarge amounts of weld metal in the weld. This is achieved throughultrasonic relaxation and redistribution of residual welding stressesand deformations, as well as by modifying welded joint materialproperties to be at the level of the base material in the area affectedby ultrasonic plastic deformations of the welded joint material.

Ultrasonic impact treatment in accordance with the invention may beapplied to the hot metal during welding, to the metal during cool downor to cold metal after welding, depending on the production conditionsand welding process.

The results of the ultrasonic impact application in accordance with theinvention are obtained by layer treatment of the weld metal, formationof the deconcentration groove in the stress concentration area, andin-process or on-line control of the ultrasonic impact treatment resultsin the course of treatment.

Ultrasonic impact treatment conditions for corner welded joints inaccordance with the invention include: ultrasonic impact frequency of upto about 1200 Hz, ultrasonic impact length of not less than about 1 ms,impact amplitude of not less than about 0.2 mm, indenter ultrasonicvibration carrier frequency of about 18 kHz and above, indenterultrasonic vibration amplitude during impact of not less than about 25μm for carbon steels and not greater than 30 μm for aluminum alloys,tool pressure against the treated surface of about 3 kg and abovesubject to manual or mechanized treatment.

(K) Liquation, Grain Size, Degassing and Pores

Welded joints made with a high volume of a molten pool under conditionsof long duration and long cooling of the weld metal are prone toliquation. This phenomenon is mainly explained by the growth of largegrains and the direction of molten pool crystallization from itsboundaries with the base metal to the center.

Ultrasonic impact treatment concluded within the parameters of theinvention during welding and cooling down of the weld metal solve thisproblem on the basis of the volume ultrasonic crystallization of themolten metal and the ultrasonic and impulse recrystallization of largegrains. Volume crystallization in the molten pool occurs due to acousticflows and enhanced cavitation caused by ultrasonic vibrationsoriginating from the ultrasonic wave propagating along the weld as aresult of the effect thereupon of ultrasonic impacts. Weld metal andnear-weld area are recrystallized under direct action of the ultrasonicimpact upon the weld and the near-weld metal being cooled down. Thisprovides specified weld metal phase homogeneity across the weld sectionin all directions. A weld joint with structural phase homogeneity can beformed in accordance with the schematic representation as shown in FIGS.17 a and 17 b wherein representative portions are enlarged. FIG. 17 aillustrates a weld having liquation 110 in the center of the weld. FIG.17 b illustrates an ultrasonic impact tool 112 treating the weld withinthe parameters of the invention to provide a weld with ultrasonic impactactivated crystallization 111. Impact is provided across the weld shownin FIG. 17 b as indicated by the arrows and the tool 112 shown in solidand broken lines.

The most important characteristics responsible for weld jointreliability, such as impact strength, yield and ultimate strengths,stringiness and crack resistance at sub-zero, and high and ambienttemperatures, depend on the grain size. Ultrasonic impact treatmentperformed within the parameters of the method at a distance from the arccorresponding to the maximum sensitivity of a molten metal to thecrystallization center formation and solidifying metal to grainrecrystallization in the process of a grain growth successfully solvesthis problem. A new type of weld joint is thus created which meets thestringent mechanical strength requirements and possesses specifiedphysical and mechanical properties because of the fine grain structureof the weld metal and heat affected zone. A schematic representation ofhow such a joint is obtained is shown in FIGS. 18 a and 18 b. FIG. 18 cgraphically illustrates the mechanical strength and impact strength,which results from ultrasonic impact treatment, for the joints. FIG. 18a shows a weld 120 (with enlarged portion for illustration) which wasnot subjected to ultrasonic impact treatment. FIG. 18 b shows a weld 121with ultrasonic impact activated crystallization (shown in theillustrative enlarged portion) by treatment with an ultrasonic impacttool 122 which moves across the weld in accordance with the arrows andtool shown in solid and broken lines. FIG. 18 c sets forth data as toweld 120 and weld 121.

One of the basic quality criteria for a welded joint is the presence orabsence of pores in the weld metal. This property is chiefly determinedby the molten pool degassing efficiency in the process of welding.Ultrasonic impact treatment in accordance with the invention makes aneffective solution for this problem possible based on the initiation ofmolten pool ultrasonic degassing in the process of welding.

This effect is achieved by ultrasonic impact treatment performed overthe weld metal or associated metal using the parameters set forth aboveat a distance from the arc that corresponds to a molten pool liquidphase, which is equivalent to the minimum solubility of gas inclusionsin the weld metal. The welded joint and a schematic representation ofits degassing are shown in FIGS. 19 a and 19 b. FIG. 19 a illustrates aweld 130 not subjected to ultrasonic impact treatment and having visiblepores in the root area of the weld. In FIG. 19 b, the weld 131 wastreated with ultrasonic impact to activate degassing so no pores arevisible. Treatment with an ultrasonic impact tool 132 is across the weldas indicated by the arrows and the tool 132 shown in solid and brokenlines.

Thus, described are three possible applications of ultrasonic impacttreatment in accordance with the invention during welding that aredirected toward producing welded joints with new properties such asliquation resistance at great volumes of molten metal, reliablerecrystallization and fine-grain structure formation, and weld metalresistance to pore formation.

Effects of ultrasonic impact treatment in accordance with the inventionupon the molten metal's behavior, structure and properties of the weldmetal and the joint as a whole are based on the corresponding methodchoice of the distance of the ultrasonic impact area from the moltenpool and the ultrasonic impact parameters. In each specific case theselection criteria of the ultrasonic impact treatment area locationperformed in accordance with the invention relative to the welding areaare the temperature ranges of effective crystallization andrecrystallization of the molten metal and weld metal respectively, aswell as the temperature range of the minimum gas solubility in themolten pool. In this case, the parameters of ultrasonic impact treatmentin accordance with the invention, subject to properties of the treatedmaterial and the temperature at the ultrasonic impact treatment area,are set within the following ranges: tool pressure from about 0.1 to 50kg, ultrasonic vibration carrier frequency at the transducer of fromabout 10 to 800 kHz, ultrasonic vibration amplitude under no-loadconditions and during impact at a carrier frequency of from about 0.5 to120 μm, tool self-oscillation amplitude of from about 0.05 to 5 mm, andthe average ultrasonic impact duration of not less than about 1 ms.

(L) Diffusion Hydrogen

Welded joints with stringent brittle fracture resistance requirementsmade of steels, specifically ferritic steels, are preliminarily orconcurrently heated before and during welding to expel diffusionhydrogen from the joint metal. This results in a high temperature at theoperator's work place, pollution of the environment and an increase inresidual welding deformations caused by the added heating of thestructure.

Ultrasonic impact treatment performed in accordance with the inventionduring welding at a distance from a molten pool and/or over cold metalof edges or after welding with intensity and spectrum of ultrasonicimpact that jointly correspond to the maximum mobility of diffusionhydrogen produces a welded joint with high resistance to brittlefracture. Thus, preliminary and concurrent heating requirements areminimized.

A schematic representation of a welded joint is shown in FIGS. 20 a and20 b. FIG. 20 c is a graph showing the minimization of residualdiffusion hydrogen content in the metal of the joint after ultrasonicimpact treatment. FIG. 20 a shows a weld 140 (with an illustrativeenlarged section) not subjected to ultrasonic impact treatment and thushas visible pores. FIG. 20 b shows weld 141 (with illustrative enlargedsection) with activated crystallization (no pores) due to the coolingdown or cold edge preparation being accompanied by ultrasonic impacttreatment using tool 142 which is moved across the weld during treatmentin accordance with the arrows and the ultrasonic impact tool 142 shownin solid and broken lines. Treatment occurs within the parametersdescribed below. FIG. 20 c shows permissible hydrogen content limits forsteel. It is conventional that prior to welding, the permissible levelof residual hydrogen in the welded joint metal should not exceed 5cm³/100 g for steel. FIG. 20 c shows the hydrogen content for the weldsshown in FIGS. 20 a and 20 b as indicated by the corresponding referencenumbers.

Ultrasonic impact treatment of welded joints in accordance with theinvention is performed, with consideration for the fact that the metalis prone to hydrogen saturation, in any production conditions: over coldedges before welding or over edges some distance ahead of the moltenpool during welding, or over the weld metal some distance following thewelding pool during welding, or over the weld metal after welding withina certain temperature range in fabrication of new structures,reengineering thereof, preventive maintenance or repair.

For all conditions referenced above, prior to treatment in accordancewith the process of the invention, the temperature range or temporaryconditions are determined that provide for effective diffusion hydrogenremoval and maintaining metal in this state.

From the saturation diagram shown in FIG. 21, it can be seen thatultrasonic impact treatment in accordance with the invention reduces thecontent of diffusion hydrogen within a wide temperature range by atleast 2 times.

Parameters of ultrasonic impact treatment in accordance with theinvention that ensure the results presented above include: ultrasonicimpact frequency of up to about 2500 Hz, ultrasonic impact amplitude ofnot less than about 0.2 mm, average statistical length of ultrasonicimpacts of not less than about 1 ms, ultrasonic vibration carrierfrequency of about 15 kHz and above, ultrasonic vibration amplitudeduring impact of not less than about 15 μm depending on the temperatureand grade of the metal being treated and not less than about 30 μm whencold metal is treated, pressing force on the tool against a treatedsurface of not less than about 5 kg for manual treatment and not lessthan about 10 kg during mechanized treatment.

(M) Aggressive Environment—Stress Corrosion (Treatment Before andDuring)

Resistance of a weld joint to stress corrosion damage or failures underfluctuating loading defines the reliability and life of a loadedstructure with a long operational cycle. Main pipelines and offshoreplatforms are examples of such structures. Their protection againststress corrosion is very costly.

Treatment to provide new properties in accordance with the inventionsolves this problem. Described below are the main parameters ofultrasonic impact treatment effect on a metal surface in aggressiveenvironment under stressed conditions or fluctuating loading:

-   -   a roughness which is not less than 5 μm at a sampling length of        0.8 mm and waviness which is not less than 15 μm at a sampling        length of 2.5 mm,    -   compressive stresses in the area of ultrasonic and impulse        deformation which are not less than the material yield strength,    -   depth of plastic deformation and introduced residual compressive        stresses which are not less than 1.5 mm, and    -   amorphous microstructure modification with the formation of a        white layer depending on the material properties which is not        less than 50 μm.

Since surface and material properties are transformed, stress corrosionresistance of the joint is increased at least by a factor of 2 ultimatecorrosion-fatigue strength increased by at least 1.3 times and the lifeincreased by at least 7 times under various loading in a corrosiveenvironment as compared to the joint in an untreated condition. It issignificant that these properties pertain equally to newly welded jointsand welded joints in operation.

The results and properties of welded joints made of steel with highcarbon content and subjected to ultrasonic impact treatment are shown inFIG. 21. It is shown in FIG. 21 that following the irregular corrosion,which is typical to occur on the surface of any material, the stableprocess occurs, wherein the corrosion rate of the layer treated byultrasonic impact treatment in accordance with the process is a minimumof 4 times less than that of the as-welded metal based on theexperimental data. A minimum equivalent time during which the carbonsteel treated by ultrasonic impact treatment in accordance with theinvention resists stress corrosion in sea water is 10 years.

Parameters of ultrasonic impact treatment in accordance with theinvention that ensure the results presented above include: ultrasonicimpact frequency of up to about 500 Hz, ultrasonic impact amplitude ofnot less than about 0.5 mm, average duration of ultrasonic impacts ofnot less than about 1 ms, ultrasonic vibration carrier frequency ofabout 15 kHz and above, ultrasonic vibration amplitude during impact ofnot less than about 20 μm, and pressing force on the tool against atreated surface of not less than about 5 kg.

(N) Holes in Welded Joints

The practice of welded structure operation is associated to a certainextent with the need to use holes as a crack arrest means in an areanear or within a welded joint. Damage in such joints may develop notonly from the crack stopped by such holes, but also from the holesthemselves. The reason is in the surface tearing produced during makingof the holes, which become stress concentration areas in operation whichin turn cause fatigue.

To obtain a reliable welded joint with crack arrest holes, ultrasonicimpact treatment in accordance with the invention is first applied toboth crack sides and then to the hole. A hole is treated where the metalis damaged during the making of the hole at the entrance and exitregions, but not less than ⅕ of the hole depth from the damaged side.Residual compressive stresses, not less than the material yieldstrength, are formed in the layer subjected to ultrasonic and impulseplastic deformation. It is noted that the indenter shape in this case ischosen to provide free access to the damaged portions of the hole.

A schematic diagram of a welded joint with holes and the results of thetreatment are shown in FIGS. 22 a and 22 b. FIG. 22 a illustrates acrack between two holes in a weld 150 prepared using conventional tipdrilling which results in known associated stresses. FIG. 22 billustrates a crack between two holes in a weld 151 prepared withconventional tip drilling followed by ultrasonic impact treatment withan impact tool 152. Associated stresses which result from the tipdrilling are altered due to formation of the compressive stress area153. FIG. 22 b also illustrates the needle indenter 154 of theultrasonic impact tool 152 and the manner of treating the holes 155 andedges of holes 156 to result in the tearing of material in the holes atthe end of the cracks. It is shown that tensile stresses in the holearea after drilling thereof are replaced by compressive stresses andpossible tensile stresses are displaced into the region of the structurewhere operational stress concentration and hence fatigue crackinitiation is unlikely to occur.

Parameters of ultrasonic impact treatment in accordance with theinvention that ensure the results presented above for a widest range ofmetals include: ultrasonic impact frequency of up to about 500 Hz,ultrasonic impact amplitude of not less than about 0.5 mm, averageduration of ultrasonic impacts of not less than about 1 ms, ultrasonicvibration carrier frequency of 15 kHz and above, ultrasonic vibrationamplitude during impact of not less than about 30 μm, pressing force onthe tool against a treated surface of not less than about 5 kg.

(O) Brackets

Weld joints of brackets with a radius cutout where a bracket planeintersects the main weld are a typical welded joint that is extensivelyused in the fabrication of welded structures. The most dangerouscomponents of such a structure are the weld ends in the cutout area andthe weld toe line when the bracket is welded to a panel. Dimensionalaccuracy in such a joint also presents a very significant problem.

Ultrasonic impact treatment of the weld along the bracket and weld endin a radius cutout when within the parameters of the invention resultsin a weld joint that meets dimensional accuracy requirements with aminimum increase in fatigue resistance of 1.3 times that of an untreatedjoint.

A schematic representation of a bracket welded joint prior to and afterultrasonic impact treatment are shown in FIGS. 23 a and 23 b. Thebracket panels 160 have cracks 161 in the areas of bracket welding inthe absence of ultrasonic impact treatment. The bracket plane intersectsthe main weld wherein a connection with the panel is made bylongitudinal fillet welds relative to the bracket end in a radiuscutout. FIG. 23 b shows a bracket treated by ultrasonic impact toprovide treatment zones 162. Ultrasonic impact treatment of the weldalong the bracket and at the weld end in the radius cutout insures thatthe welded joint meets dimensional accuracy requirements and results ina minimum increase in fatigue resistance of 1.3 times as compared to thesame properties in an untreated bracket structure.

When the weld end in the cutout area is treated by ultrasonic impacttreatment in accordance with the invention special tool heads are usedto provide an access for the indenter to this area.

Parameters of ultrasonic impact treatment in accordance with the processof the invention which ensure the results presented above for a widestrange of metals include: ultrasonic impact frequency of up to about 300Hz, ultrasonic impact amplitude of not less than about 0.5 mm, averageduration of ultrasonic impacts of not less than about 1 ms, ultrasonicvibration carrier frequency of about 15 kHz and above, ultrasonicvibration amplitude during impact of not less than about 30 μm, pressingforce on the tool against the treated surface of not less than about 3kg.

(P) Welded Joints Prone to Martensite Formation

When residual welding deformation should be minimized, intense forcedcooling of a welded joint immediately following the welding process isused in some specific cases. This causes a well-known hardening effect,especially in carbon steels, that is accompanied by expelling martensiteand the formation of a joint having limited ductility. Martensitedecomposition is achieved by additional forced heating of the joint andsoaking of the joint for a long time within a narrow specifiedtemperature range. This procedure has a large energy consumption, iscomplex as regards achieving the conditions of heating and soakingwithin the narrow temperature range and is characterized by insufficientconsistency of results.

Ultrasonic impact treatment of this type of joint within the parametersof the invention at a distance from the heating arc corresponding to thetemperature of martensite decomposition and its replacement by sorbiteor tempered martensite, changes the welded joint structure in atemperature range which is a minimum of 1.5 times greater than thebottom boundary of this range, while the range itself is a minimum 2times greater than that required in welding to reduce the likelihood ofmartensite formation under the above-mentioned conditions in the absenceof ultrasonic impact treatment. As this takes place, the martensitedecomposition time is reduced by at least 10 times. This produces a weldjoint with a radically increased process temperature range of martensitedecomposition, while the average temperature of the range is reducedrelative to standard conditions required to solve this problem.

A diagram of supercooled austenite (martensite) decomposition is shownin FIG. 24 for an exemplary sample of steel 12XH3. Lines 1 indicatemartensitic transformation at a temperature T1 for a sample notsubjected to ultrasonic treatment. A sample, as indicated by lines 2,subjected to ultrasonic impact treatment according to the invention hasmartensitic transformation at temperature T2. T1>T2. It is shown in FIG.24 that the martensite decomposition process during standard heattreatment can occur within the temperature range from 495° to 430° C.for a minimum of 3 hours. During ultrasonic impact treatment inaccordance with the invention the same process can last for 3-4 min.within the temperature range of 260° to 39020 C.

Parameters of ultrasonic impact treatment in accordance with theinvention that ensure the results presented above for a widest range ofmetals include: ultrasonic impact frequency of up to about 800 Hz,ultrasonic impact amplitude of not less than about 0.5 mm, averageduration of ultrasonic impacts of not less than about 1 ms, ultrasonicvibration carrier frequency of about 15 kHz and above, ultrasonicvibration amplitude during impact of not less than about 30 μm, pressingforce on the tool against a treated surface of not less than about 10kg.

This produces a weld joint with a radically increased processtemperature range of martensite decomposition, while the averagetemperature of the range is reduced relative to a standard conditionsrequired to solve this problem within a period of the actual flow-lineautomatic or computer-aided production of welded structures.

(Q) Welded Joints with Protective and/or Hardening Coating

The maintenance of welded joints is associated in many respects with theneed for their protection or hardening by using various metallic ornonmetallic coatings. In such a case, the use of any type of mechanicaloperation, including the known methods of plastic deformation of theweld, near-weld area and weld toe, is limited by the coating integrityrequired.

Treating with ultrasonic impact in accordance with the invention solvesthe above problem and makes it possible to produce welded joints withspecified new properties since the ultrasonic impact treatment can beconducted over the coating. In this case, the integrity and improvementin properties of protective or hardening coatings are obtained alongwith specified properties in the welded joint.

An example of such a welded joint is shown in FIGS. 25 a, 25 b and 25 c.FIG. 25 a illustrates a weld before coating and ultrasonic impacttreatment. FIG. 25 b illustrates the same weld after a coating 170 isapplied and before ultrasonic impact treatment of the coated weld. InFIG. 25 c, the coated weld is shown following ultrasonic impacttreatment. The groove and stress raiser modification in the weld isdenoted by 171 over the coating 170. In the weld joint of FIG. 25 c, theradius is a minimum of 0.5 mm, the width is up to 10 mm, the depth is upto 2 mm, and the coating thickness is 0.15 mm when the web thickness is4 mm. It is shown in FIGS. 25 a-25 c that ultrasonic impact treatment inaccordance with the invention makes possible the process of producing awelded joint with specified properties due to the use of special coatingin the following order: fabrication of a joint by welding, applicationof the protective or hardening coating, and ultrasonic impact treatmentin accordance with the invention.

To maintain the coating integrity, the conditions of ultrasonic impacttreatment in accordance with the invention are selected so that thecontact pressure on the coated surface and pressure gradients in theultrasonic impact treatment area are not greater than the breakingstrength of the coating.

Parameters of ultrasonic impact treatment in accordance with theinvention that ensure the results presented above for a widest range ofmetals include: ultrasonic impact frequency of up to about 1500 Hz,ultrasonic impact amplitude of not less than about 1 mm, averageduration of ultrasonic impacts of not less than about 1 ms, ultrasonicvibration carrier frequency of not less than about 20 kHz, ultrasonicvibration amplitude during impact of not greater than about 30 μm,contact pressure and stress gradient at the boundary between individualultrasonic impact treatment tool marks of not greater than the coatingbreaking strength, pressing force on the tool against a treated surfaceof not less than about 3 kg.

(R) Welded Structures

The above described welded joints, and processes for obtaining thejoints, make possible the creation of welded structures that meet highquality and reliability requirements. A structural representation isschematically shown in FIG. 26 to illustrate various welded joints 180obtainable under the invention. Such structures in aggregate or in anycombination of elements, details, joints and materials may include:panels, cylindrical elements with continuous or varying bevel angle thatare welded perpendicularly or at an angle to the panel, flat structuralelements, webs, brackets, corner joints, lap joints, etc. The qualityand reliability of the welded joints are improved by provision ofimproved properties in the joints through ultrasonic impact treatment ofthe joints in accordance with the invention.

As will be apparent to one skilled in the art, various modification canbe made within the scope of the aforesaid description. Suchmodifications being within the ability of one skilled in the art form apart of the present invention and are embraced by the appended claims.

1. An ultrasonic impact treated non-detachable welded joint comprisingat least one predetermined structural property resulting from ultrasonicimpact treatment of said welded joint, said at least one predeterminedstructural property including at least one of: surface roughness andrelief of at least about 0.1 μm; a radius between surfaces of at leastabout 0.5 mm; a depth of a groove along a weld toe line or line betweenany surfaces in a stress concentration area of up to about 2 mm with awidth of said groove being up to about 10 mm; increase of materialmechanical properties in a stress concentration area, as to strength byat least about 1.5 times and impact strength by at least about 1.2times; plastic deformation, favorable compressive stresses and afavorable relative change in microhardness to a depth of up to about 7mm; distribution of elastic compressive stresses due to plasticdeformation of material in section normal to a surface to a depth of upto 10 mm; relaxation of process induced residual stresses due toultrasonic fluctuating stress wave with an amplitude of at least about0.05 of a material yield strength, to a depth of up to about 12 mm;favorable residual stresses of a first and a second kind on and under asurface to a predetermined depth of at least material yield strength andultimate strength based on task application; compensation for residualprocess induced deformations by at least about 40% of those occurringwithout ultrasonic impact treatment application with increased stresscorrosion resistance by up to about 10 times; increase incorrosion-fatigue strength by up to about 2.5 times and a life span in acorrosion environment of up to about 20 times under variable loading;increase in fatigue limit in air under repeated or fluctuating stress byat least about 1.5 times and a life span by at least about 10 times toincrease joint strength by at least 1 category; or formation of a whitelayer and an amorphous structure to a depth of at least about 50 μm. 2.The ultrasonic impact treated non-detachable welded joint according toclaim 1, wherein said welded joint is made of a high strength steel oralloy having a yield strength of σ>500 MPa following ultrasonic impacttreatment and has a fatigue limit which is a minimum of about 30%greater than that of a steel or alloy with σ<500 MPa.
 3. The ultrasonicimpact treated non-detachable welded joint according to claim 1, whereinsaid favorable compressive stresses have a depth of about 2 mm, with amagnitude at a surface greater than a yield strength and a fatigue limitof an untreated base material of the welded joint by a factor of up toabout 1.5.
 4. The ultrasonic impact treated non-detachable welded jointaccording to claim 1, wherein said welded joint has a level of residualstresses of about 0.5 less of a yield strength of said welded joint;residual welding deformations of about 100% or less of a dimensionaltolerance predetermined for said welded joint; and/or fatigue resistanceequal to or greater than that of an untreated base material of saidwelded joint.
 5. The ultrasonic impact treated non-detachable weldedjoint according to claim 1, wherein said fatigue limit of a spot weld isincreased by at least about 1.3 times that of an untreated base materialand has increased fatigue resistance, yield point, ultimate strength andimpact strength to a level equal to or greater than that of an untreatedbase metal material of the welded joint.
 6. The ultrasonic impacttreated non-detachable welded joint according to claim 1, wherein saidfatigue limit of a tack weld is at least about 1.3 times greater thanthat of an untreated base material of the welded joint and fatigueresistance, ultimate strength and impact strength are equal to orgreater than that of the untreated base material.
 7. An ultrasonicimpact treated non-detachable welded joint comprising structuralproperties resulting from ultrasonic impact treatment of said weldedjoint wherein parameters of said treatment include oscillating systemfrequency of greater than zero to about 800 kHz, pressure on anultrasonic impact tool of greater than zero to about 50 kg, ultrasonictransducer vibrational amplitude during impact of greater than 0 toabout 120 μm, ultrasonic frequency in a range of greater than zero toabout 2500 Hz, self-oscillation amplitude of the impact tool of greaterthan zero to about 5 mm, and an average duration of impact of saidultrasonic impact tool being at least about 1 ms.
 8. An ultrasonicimpact treated non-detachable welded joint comprising steel or steelalloy having a yield strength of σ>500 MPa, and structural propertiesresulting from ultrasonic impact treatment of said welded joint whereinparameters of said treatment include an oscillating system frequency ofabout 27 kHz, pressure on an ultrasonic impact tool of greater than zeroto about 10 kg, ultrasonic transducer vibrational amplitude duringimpact of at least about 30 μm, ultrasonic frequency in a range of about80-250 Hz, self-oscillation amplitude of the impact tool of greater thanzero to about 2 mm, indenter diameter of about 3-6.35 mm, and length ofindenter being in a range of about 10-35 mm, wherein said welded jointhas favorable compressive stresses to a depth of at least 2 mm.
 9. Anultrasonic impact treated non-detachable welded joint with improvedstress concentration comprising a groove in a transition area between aweld material and a base material, said groove having radiuses at aboundary of the groove of at least about 0.5 mm, widths greater thanzero to about 10 mm and depth of greater than zero to about 2 mm, andproperties resulting from ultrasonic impact treatment of the weldedjoint wherein parameters of said treatment include ultrasonic vibrationamplitude during impact of greater than zero to about 50 μm at afrequency of greater than zero to about 80 kHz, ultrasonic frequency ofgreater than zero to about 500 Hz, self-oscillation amplitude of anultrasonic impact tool of at least about 0.2 mm, an off-duty factor ofimpact impulses of greater than zero to about 0.5, and pressure on theultrasonic impact tool of at least about 3 kg.
 10. An ultrasonic impacttreated non-detachable welded joint with improved external loadingproperties comprising a joint metal of carbon structural steel,stainless steel, or aluminum and titanium alloys, and propertiesresulting from ultrasonic impact treatment of the welded joint whereinparameters of said treatment include ultrasonic vibration amplitudeduring impact of greater than zero to about 50 μm at a frequency ofgreater than zero to about 80 kHz, ultrasonic frequency of greater thanzero to about 500 Hz with average duration being at least about 1 ms,self-oscillation amplitude of an ultrasonic impact tool of at leastabout 0.2 mm, and pressure on the ultrasonic impact tool of at leastabout 3 kg, whereby compressive stresses and strength in a stressconcentration area of the joint is greater than that present in thejoint in the absence of ultrasonic impact treatment to compensate forexternal operational forces which cause in-service cracking.
 11. Thewelded joint of claim 10 wherein said ultrasonic impact treatmentincludes ultrasonic impact of a weld toe of said welded joint and aload-carrying component on a loading side providing during treatmentplastic deformation to create and distribute said compressive stresses.12. An ultrasonic impact treated non-detachable welded joint comprisinga welded joint with compressive stresses in a plastic deformation areato a depth of at least about 2 mm and corresponding compressive stressesin an elastic deformation area sufficient to compensate for residualeffect of the tensile stresses, and properties resulting from ultrasonicimpact treatment of the welded joint wherein parameters of the treatmentinclude pressure force of an ultrasonic impact tool of greater than zeroto about 10 kg, ultrasonic impact frequency of greater than zero toabout 500 Hz, average duration of ultrasonic impact of at least about 1ms, ultrasonic carrier frequency of greater than zero to about 100 kHz,ultrasonic oscillation amplitude of an indenter during impact of atleast about 30 μm, and impact amplitude of at least about 0.2 mm.
 13. Anultrasonic impact treated non-detachable welded joint comprisingdeformation compensation within said joint to a value of 1>K_(o)>−1wherein K_(o) is a toolmarks overlap coefficient, and propertiesresulting from ultrasonic impact treatment of the welded joint whereinparameters of the treatment include pressure force of an ultrasonicimpact tool of at least about 4 kg, ultrasonic impact frequency of atleast about 100 Hz, impact amplitude of at least about 0.2 mm, averageimpact duration of at least about 1 ms, carrier ultrasonic frequency ofat least about 15 kHz, ultrasonic vibration amplitude during impact ofat least about 30 μm when said welded joint is made of steel or steelalloy and about 30 μm or less when said welded joint is made of analuminum alloy or metal with a yield strength of up to about 235 MPa.14. The welded joint according to claim 13 wherein said propertiesinclude modification of residual welding deformations to create rigidattachment with subsequent ultrasonic relaxation of residual weldingstresses, or ultrasonic plastic deformation and redistribution of theweld metal.
 15. An ultrasonic impact treated non-detachable welded jointincluding residual stresses of not greater than 0.5 of the yieldstrength of the welded joint, residual welding deformations of notgreater than 100% of dimensional tolerance specific to said weldedjoint, and fatigue resistance of the welded joint is not less than thefatigue resistance of a base metal in said welded joint, whereinparameters of ultrasonic impact treatment of said welded joint includepressure upon an ultrasonic impact tool with a steel indenter is atleast about 3 kg during manual treatment and greater than zero to about20 kg during mechanized treatment, ultrasonic impact frequency of atleast about 0.2 mm, carrier frequency of indenter ultrasonic vibrationsof at least about 15 kHz, and ultrasonic vibration amplitude duringimpact of at least about 20 μm when metal is above ambient temperatureduring treatment and at least about 30 μm when metal is at or aboutambient temperature during treatment.
 16. An ultrasonic impact treatednon-detachable welded joint comprising a steel joint structured as acorner joint with obtuse flank angles for a weld metal of the joint,said corner joint being resistant to root cracking based on ultrasonicimpact treatment of said welded joint within parameters includingpressure force of an ultrasonic impact tool of at least about 3 kgduring manual treatment or at least about 25 kg during mechanizedtreatment, ultrasonic frequency of greater than zero to about 800 Hz,ultrasonic impact amplitude of at least about 0.2 mm, ultrasonicvibration carrier frequency of at least about 18 kHz, ultrasonicvibration amplitude during impact of greater than zero to about 20 μm ata temperature above about 400° C., and average ultrasonic impactduration of at least about 1 ms, whereby weld metal is redistributedbetween a flange and a web in the corner joint.
 17. The welded joint ofclaim 16 wherein said ultrasonic treatment provides a meniscus and fusessharp edges of said welded joint such that upon solidification followingsaid treatment smooth transitions are provided between a weld and a basemetal of said welded joint increasing, to a level greater than saidjoint prior to treatment, joint properties of resistance to stressconcentration and fatigue crack formation in a root of the weld.
 18. Anultrasonic impact treated non-detachable welded joint comprising acarbon steel or aluminum alloy spot welded joint with displaced tensilestress based on ultrasonic impact treatment of said spot welded jointwithin parameters including ultrasonic impact frequency of at leastabout 80 Hz, average impact duration of least about 1 ms at an amplitudeof at least about 0.2 mm, indenter ultrasonic vibration carrierfrequency during impact of greater than zero to about 100 kHz,ultrasonic vibration amplitude during impact in a range of from about5-40 μm, and pressure force on an impact tool of from about 3-30 kg. 19.An ultrasonic impact treated non-detachable welded joint comprising ajoint of carbon steel or aluminum alloy with a tack weld or a lap weldresistant to cracking at weld ends based on ultrasonic impact treatmentof said welded joint within parameters including ultrasonic impactfrequency of greater than zero to about 2000 Hz, average duration ofultrasonic impact of at least about 1 ms, impact amplitude of at leastabout 0.2 mm, indenter ultrasonic vibration carrier frequency of atleast about 18 kHz, indenter ultrasonic vibration amplitude duringimpact of at least about 25 μm for carbon steel and greater than zero toabout 30 μm for aluminum alloy, and pressure force of an ultrasonicimpact tool against a treated surface of at least about 3 kg.
 20. Anultrasonic impact treated non-detachable welded joint comprising acorner welded joint of carbon steel or aluminum alloy having increasedfatigue limit by at least a factor of at least 1.3 based on ultrasonicimpact treatment of said corner welded joint within parameters includingultrasonic impact frequency of greater than zero to about 1200 Hz,average duration of ultrasonic impact of at least about 1 ms, ultrasonicimpact amplitude of at least about 0.2 mm, indenter ultrasonic vibrationamplitude during impact of at least about 25 μm for carbon steel and notgreater than about 30 μm for aluminum alloy, pressure of an ultrasonicimpact tool against a treated surface of said welded joint of at leastabout 3 kg.
 21. An ultrasonic impact treated non-detachable welded jointcomprising a welded joint having weld metal structure phase homogeneityin all directions in the weld based on crystallization andrecrystallization of the weld metal based on ultrasonic impact treatmentof the welded joint within parameters including pressure of anultrasonic impact tool of from about 0.1-50 kg, ultrasonic vibrationcarrier frequency at a transducer of from about 10-800 kHz, ultrasonicvibration amplitude under no-load conditions and during impact of anultrasonic tool at a carrier frequency of from about 0.5-120 μm,self-oscillation amplitude of ultrasonic impact tool of from about0.05-5 mm, and average duration of ultrasonic impact of at least about 1ms.
 22. An ultrasonic impact treated non-detachable welded jointcomprising a joint of ferritic steel with a weld having activatedcrystallization and resistance to brittle fracture based on ultrasonicimpact treatment of the welded joint within parameters includingultrasonic impact frequency of greater than zero to about 2500 Hz,ultrasonic impact amplitude of at least about 0.2 mm, average durationof ultrasonic impacts of at least about 1 ms, ultrasonic vibrationcarrier frequency of at least about 15 kHz, ultrasonic vibrationamplitude during impact of at least about 15 μm for metal not at ambienttemperature and less than about 30 μm for treatment of metal at or aboutambient temperature, and pressure force of an ultrasonic impact toolagainst a treated surface of at least about 5 kg for manual treatment orat least about 10 kg for mechanized treatment.
 23. An ultrasonic impacttreated non-detachable welded joint comprising a joint modified byultrasonic impact to increase resistance to stress corrosion to a levelgreater than said joint untreated by ultrasonic impact, based onultrasonic impact treatment of the welded joint within parametersincluding ultrasonic impact frequency of greater than zero to about 500Hz, ultrasonic impact amplitude of at least about 0.5 mm, averageduration of ultrasonic impacts of at least about 1 ms, ultrasonicvibration carrier frequency of at least about 15 kHz, ultrasonicvibration amplitude during impact of at least about 20 μm, and pressureforce on an ultrasonic impact tool against a treated surface of at leastabout 5 kg.
 24. The welded joint according to claim 23 wherein saidjoint has a surface roughness of not less than about 5 μm in a samplinglength of 0.8 mm, a waviness of not less than about 15 μm at a samplinglength of 2.5 mm, compressive stresses not less than yield strength ofthe joint, depth of plastic deformation and induced residual stresses ofnot less than about 1.5 mm, corrosion resistance of at least 2 timesgreater than in absence of the treatment, and corrosion-fatigue strengthof not less than about 1.3 times that of the joint in absence of thetreatment of the joint.
 25. An ultrasonic impact treated non-detachablewelded joint comprising a welded joint structure containing at least onecrack arrest hole in said structure, said at least one crack arrest holehaving compressive stresses in the structure surrounding the at leastone hole, wherein parameters of ultrasonic impact treatment of saidwelded joint structure containing said at least one crack arrest holeinclude ultrasonic impact frequency of greater than zero to about 500Hz, ultrasonic impact amplitude of at least about 0.5 mm, averageduration of ultrasonic impacts of at least about 1 ms, ultrasonicvibration carrier frequency of at least about 15 kHz, ultrasonicvibration amplitude during impact of at least about 30 μm, and pressureforce on an ultrasonic impact tool against a treated surface of at leastabout 5 kg.
 26. An ultrasonic impact treated non-detachable welded jointcomprising a structural combination including a welded joint with abracket and a panel, wherein a radius cutout is present between thebracket and the panel, said structural combination has fatigueresistance of at least 1.3 times that of the structural combination whenuntreated by ultrasonic impact treatment, wherein said ultrasonic impacttreatment of said structural combination is within parameters includingultrasonic impact frequency of greater than zero to about 300 Hz,ultrasonic impact amplitude of at least about 0.5 mm, average durationof ultrasonic impacts of at least about 1 ms, ultrasonic vibrationcarrier frequency of at least about 15 kHz, ultrasonic vibrationamplitude during impact of at least about 30 μm, and pressure force onan ultrasonic impact tool against a treated surface of at least about 3kg.
 27. An ultrasonic impact treated non-detachable welded jointcomprising a welded joint with reduced martensite decomposition based onultrasonic impact treatment of the welded joint within parametersincluding ultrasonic impact frequency of greater than zero to about 800Hz, ultrasonic impact amplitude of at least about 0.5 mm, averageduration of ultrasonic impacts of at least about 1 ms, ultrasonicvibration carrier frequency of at least about 15 kHz, ultrasonic impactof at least about 30 μm, and pressure force on an ultrasonic impact toolagainst a treated surface of at least about 10 kg.
 28. An ultrasonicimpact treated non-detachable welded joint comprising a welded jointhaving a coating thereon, said coating being resistant to breakage uponultrasonic impact treatment wherein said treatment has parameters whichinclude ultrasonic impact frequency of greater than zero to about 1500Hz, ultrasonic impact amplitude of at least about 1 mm, average durationof ultrasonic impacts of at least about 1 ms, ultrasonic vibrationcarrier frequency of at least about 20 kHz, ultrasonic vibrationamplitude during impact of greater than zero to about 30 μm, contactpressure and stress gradient at a boundary between individual ultrasonicimpact tool marks of not greater than coating breaking strength, andpressure force on an ultrasonic impact tool against a surface of atleast about 3 kg.
 29. Process of analyzing and selecting an ultrasonicimpact treatment for treating a welded joint to have one or morepredetermined properties, comprising (1) defining pre-treatmentproperties of material forming a weld of the joint and the welded jointitself; (2) defining conformity of the properties of (1) topost-treatment properties to be provided in the joint; (3) definingphysical factors having an effect on the joint in context of thepost-treatment properties to be provided in the joint; (4) definingpositive result criteria and effect of ultrasonic impact treatment onproviding the post-treatment properties in the joint; (5) defining amanner of ultrasonic impact treatment for the joint in context ofproviding the post-treatment properties in the joint, including definingultrasonic impact treatment conditions in combination with parameters ofa transducer, ultrasonic impact, indenter, pressure, mechanicalproperties and acoustic characteristics of the material to be treated;and (6) conducting ultrasonic impact treatment on the joint inaccordance with the definitions established in (1) to (5).
 30. Processaccording to claim 29, wherein said physical factors of (3) comprise oneor more of plastic deformation caused by low frequency impact,ultrasonic plastic deformation during said impact treatment, amplitudeand attenuation of ultrasonic stress wave in the material of the joint,and temperature and heat rejection rate at a contact point duringultrasonic impact.
 31. Process according to claim 29, wherein saidpost-treatment properties of (2) comprise one or more of geometricaccuracy, residual deformations and nominal dimension tolerance thereof,residual stresses equilibrated within volume of the joint and structuralsegments of the material of the joint, acceptable stress concentrationlevel and configuration of stress raisers responsible for load-carryingcapacity of the joint, fatigue limit and fatigue resistance underlow-cycle and high-cycle reversal and fluctuating loading, fatigue limitand resistance to corrosion and corrosion fatigue failures in aggressiveenvironment under the low-cycle and high-cycle reversed and fluctuatingloading and properties of the welded joint.
 32. Process according toclaim 29, wherein the criteria of (4) comprise one or more of inducedresidual stress and deformation levels; relief, roughness and geometricmodification of surface and transitional areas of the joint andmodification of properties of the material in an area of treatment;relaxation and redistribution of residual stresses produced duringmanufacture of the joint prior to impact treatment; and modification ofthe joint as to type and conditions of resistance to a service load. 33.Process according to claim 29, wherein the parameters of (5) compriseone or more of pressure on an ultrasonic impact tool being in a range offrom about 0.1-50 kg; carrier ultrasonic frequency of the transducerbeing between about 10-800 kHz; amplitude of ultrasonic vibrations atsaid carrier frequency of between about 0.5-120 μm; ultrasonic impactfrequency and self-oscillation frequency of the tool being between about5-2500 Hz with duration of random ultrasonic impact in a range of fromabout 2-50 vibration periods at carrier ultrasonic frequency;self-oscillation amplitude of the tool being between about 0.5-5 mm;level of connection between a freely axially moving indenter and atransducer of the tool being within the claimed parameters; freeultrasonic impacts within said parameters selected in view of task,property and size requirements of the material and the joint. 34.Process of treating a non-detachable welded structure comprising: (a)subjecting at least a portion of a weld in a non-detachable weldedstructure to repeated ultrasonic impact by an ultrasonic impact tool tocause controlled plastic deformation in said weld and modify surface andtransitional areas of the weld of said welded structure and thus modifyone or more material properties in the welded structure; (b) obtainingthe material properties of (a) by controlling one or more selectparameters of said repeated ultrasonic impact, said select parametersbeing selected from one or more parameters of the group consisting of(1) pressure on the ultrasonic impact tool being in a range of fromabout 0.1-50 kg; (2) ultrasonic frequency of the ultrasonic impact toolbeing from between about 10-800 kHz; (3) amplitude of vibrations fromsaid ultrasonic impact being from between about 0.5-120 μm; (4)ultrasonic frequency of the ultrasonic impact tool and self-oscillationfrequency of the ultrasonic impact tool being from between about 5-2500Hz with a duration of ultrasonic impact being in a range of from about2-50 vibration periods at a carrier ultrasonic frequency; (5)self-oscillation amplitude of the ultrasonic impact tool being frombetween about 0.05-5 mm; (6) a connection level between a freely axiallymoving indenter of the ultrasonic impact tool and a transducer of theultrasonic impact tool acting within parameters (1)-(5); and (7) freeultrasonic impacts falling within parameters (1)-(5) based on task,properties and size of the welded structure.
 35. Process of tuningultrasonic impact for ultrasonic impact treatment of a non-detachablewelded joint comprising controlling in combination parameters of freeultrasonic impact of the treatment, wherein said parameters are ofpressing, amplitude, frequency, and duration of the free ultrasonicimpact together with control of transducer vibrations from said impact.36. Process of structural rearrangement of a welded joint comprisingsubjecting at least part of the welded joint to random ultrasonic impactwhile controlling amplitude, length and repetition rate of saidultrasonic impact in a manner to impact energy at a repetitive rate withpauses between impacts, said pauses being sufficient for relaxation ofmaterial condition and availability for next impact with minimalresistance that does not exceed internal losses in the material when thematerial is in a quiet condition.
 37. Process according to claim 34,wherein the welded structure is selected from the group consisting ofbutt joints, fillet joints, lap joints, narrow gap joints, spot jointsand apertures in a joint structure.
 38. Process according to claim 35,wherein the welded structure is selected from the group consisting ofbutt joints, fillet joints, lap joints, narrow gap joints, spot jointsand apertures in a joint structure.
 39. Process according to claim 36,wherein the welded structure is selected from the group consisting ofbutt joints, fillet joints, lap joints, narrow gap joints, spot jointsand apertures in a joint structure.
 40. Process according to claim 34,wherein the material properties affected are one or more propertiesselected from a group consisting of surface roughness and relief, radiuspresent between surfaces, depth of groove at a weld toe line or a linebetween surfaces of stress concentration area, width of said groove,impact strength, plastic deformation, compressive stresses, ultrasonicfluctuating stresses, residual stress, stress corrosion, whitelayer/amorphous structure formation, and corrosion fatigue.